For paper-making machines, shoe press devices, in which a press unit constituting of a press roll and a shoe, has been used ordinarily. Since the shoe press device is able to provide a planar press unit, inherent effects are shown at a variety of portions in paper-making processes in comparison with existing linear press parts composed of rolls themselves.
FIG. 1 shows a schematic view of a conventional shoe press device used in a press part. In a device of FIG. 1(a), a relatively elongated shoe press belt is used and in a device of FIG. 1(b), a relatively short shoe press belt is used.
The shoe press devices 100a, 100b of FIGS. 1(a) and (b) comprises a press unit P constituted of a press roll R and a shoe S, respectively. A pair of felts F, which sandwich wet paper W therebetween, and belt B are disposed in the press unit, and the rotation of the press roll R allows the wet paper W, felts F, F and belt B to run and pass through the press unit P.
It will be noted that arrow MD in the figures indicates the direction of rotation of the press roll R.
FIG. 2 shows a schematic view of a conventional shoe press device used in a calendar part.
A shoe press device 100c employed in the calendar part shown in FIG. 2 holds a belt BC for calendar and a rough surface paper W′ as a paper material in a press unit P which is constituted of a calendar roll R′ and a shoe S, and the rotation of the calendar roll R′ allows the belt BC for calendar and the rough surface paper W′ to pass through the press unit P.
It will be noted that arrow MD in the figure indicates the direction of rotation of the press roll R.
A belt B and a belt BC for calendar are used in the shoe press devices for the press part and the calendar part. The belt B and the belt BC for calendar differ in structure in details so that they show inherent effects at the respective parts. Nevertheless, they have a common fundamental structure composed of a base member for ensuring strength throughout the belt and a polymer elastic part disposed at the base member.
Meantime, even with the shoe press device in either part, it is common to be formed with means of supplying a lubricant to reduce a friction between shoe and belt. Liquid lubricant oil is used as the lubricant.
However, these shoe press devices are disadvantageous in that when a lubricant is supplied between the shoe and the belt in reduced amount, a shortage of the lubricant is apt to occur, thereby causing the belt to be damaged owing to the heat of friction.
The trouble of a lubricant supply device may lead to no supply of lubricant, which cause a breakage of the belt likewise.
To cope with this situation, many attempts have been proposed for supplying a large amount of a lubricant between the shoe and the belt with respect to the machine configuration of shoe press device. Further, many attempts have been proposed for supplying a larger amount of a lubricant into the press part also with respect to the belt configuration.
FIG. 3 shows a system of supplying a lubricant to a press part of a shoe press device disclosed in Patent Document 1.
FIG. 3(a) shows a lubricant supply device L, which is located at an upstream side along the direction of MD relative to a shoe S so as to supply a lubricant L1 between the shoe S and a shoe contact surface B12 of a belt B1.
This invention is characterized by providing a plurality of concave portions B13 for holding a lubricant in the surface of the shoe contact surface B12 of the belt B1. The belt B1 is run toward under nip pressure while keeping a lubricant by means of the concave portions B13, thus enabling the lubricant to be supplied between the shoe S and the belt B1.
In this Patent Document 1, a variety of configuration examples of concave portions are described, and for example, a cup-shaped concave portions B13 as shown in FIG. 3(b) and a grooved concave portions B13′ as shown in FIG. 3(c) are disclosed.
On the other hand, FIG. 4 shows a belt disclosed in Patent Document 2. In this technique, a belt B2 is constituted of a base member consisting of MD yarns B24 and CMD yarns B25, which are laid one on another, and a polymer elastic part disposed on the base member. The belt B2 has a wet paper contact surface B21 and a shoe contact surface B22.
It is to be noted that the CMD indicates a direction vertical to the MD on the plane of the belt.
On the belt B2, convex portions 823 are formed at the shoe contact surface 822. These convex portions 23 allow concaves and convexes to be formed at the shoe contact surface B22. In this way, a lubricant is held at the shoe contact surface B22, thereby enabling the lubricant to be supplied between the shoe and the belt B2.
Further, FIG. 5 shows a belt disclosed in Patent Document 3. This belt 10 has a wet paper contact surface 11 and a shoe contact surface 12 at a base member 20 wherein fine irregularities are formed at the shoe contact surface 12 by means of a powder 40 contained in a polymer elastic part 30. A lubricant is held in these fine irregularities, so that a friction between the shoe and the belt is mitigated.    Patent Document 1: U.S. Pat. No. 4,482,430    Patent Document 2: JP, A 06-81291    Patent Document 3: JP, A 2004-84125